The present disclosure relates to a vehicle air conditioner including a heat pump device which performs heating and defrosting modes of operation.
A vehicle air conditioner with a heat pump device has been mounted on a car and other kinds of vehicles (see, for example, Japanese Unexamined Patent Publication No. 2010-111222). The heat pump device includes a compressor, an interior heat exchanger, an expansion valve, and an exterior heat exchanger. An interior fan to blow air toward the interior heat exchanger is provided inside the vehicle cabin, and an exterior fan to blow air toward the exterior heat exchanger is provided outside the vehicle cabin.
During heating, the interior heat exchanger functions as a radiator, and the exterior heat exchanger functions as a heat absorber. If frost is formed on the exterior heat exchanger during heating, the operation modes are switched into a defrosting operation mode to supply a high-temperature refrigerant to the exterior heat exchanger. According to Japanese Unexamined Patent Publication No. 2010-111222, the exterior fan is stopped during the defrosting mode of operation, and when the defrosting mode of operation ends, the airflow rate of the exterior fan is maximized to blow off the water deposited on the exterior heat exchanger.
While the defrosting mode of operation is being performed, the frost formed on the exterior heat exchanger melts and turns into water. However, if the exterior fan is stopped as in Japanese Unexamined Patent Publication No. 2010-111222 when the frost turns into water, the water will be left in the fins of the exterior heat exchanger and will exchange heat with a high-temperature refrigerant flowing through the heat-transfer pipe of the exterior heat exchanger to remove heat from the high-temperature refrigerant. Thus, the quantity of heat it takes to melt the frost decreases so much that it takes a long time to finish defrosting, thus affecting the comfortableness of the occupant, which is a problem. Particularly when the outside air temperature is as low as 0° C. or less, a significant quantity of heat is removed from the refrigerant to make this problem a serious one.
In addition, the exterior heat exchanger is rarely frosted uniformly, if ever, and in most cases, has an easily defrostable region and a non-easily defrostable region. Furthermore, depending on the configuration and operating state of the heat pump device, sometimes a region closer to refrigerant outlet of the exterior heat exchanger may be frosted more easily than another region closer to refrigerant inlet thereof.
In view of the foregoing background, it is therefore an object of the present disclosure to increase the occupant's comfortableness by shortening the time for defrosting with the decrease in the quantity of heat of the refrigerant minimized by draining efficiently the water collected in the exterior heat exchanger during a defrosting mode of operation.